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Double Tsunami, Double Destruction: Merging Tsunamis of the 2011 Tohoku-Oki

Earthquake Observed Over Open Ocean

Y. Tony Song & Ichiro Fukumori, NASA Jet Propulsion Laboratory Yuchan Yi & C. K. Shum, Ohio State University

2011 AGU Fall Meeting Dec. 5, 2011

Tony Song, Dec 2011

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The Problem

Tony Song, Dec 2011

Tang et al. (2008): Model tsunami maximum height of the 2006 Tonga earthquake

• Tsunamis often severely devastate some coastal areas while leaving others with little damage.

• This unpredictability complicates efforts to make accurate and timely tsunami forecasts that can be used to evacuate coastal communities.

Two Challenges: Near-field forecast: To save lives,

early warnings (~10 minutes after the quake) are needed.

Far-field forecast: To avoid unnecessary panic and economic loss, precise information on strike locations is needed.

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What Are Merging Tsunamis ?

Tony Song, Dec 2011

Woods & Okal (1987): Ray-tracing model of the 1960 Chilean tsunami

The 1960 Chilean tsunami killed many people far from the earthquake, 142 in Japan and 61 in Hawaii.

Scientists believe its tremendous destructive power at long distances from the epicenter is the result of a “merging tsunami” that amplified the waves and allowed them to remain damaging.

Since then, scientists have been searching for evidence of merging tsunamis.

The 2011 Japanese tsunami models show similar “merging tsunamis” or “tsunami jets,” traveling long distances without reducing their power.

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Our Research Methodology

Tony Song, Dec 2011

Step 3: The ocean model was matched with observations from satellites

Step 2: A 3-D ocean model was used to replicate the March 11, 2011 tsunami

Step 1: Data from 1,200 GPS stations were used to derive the tsunami source

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Matching Models With Satellite Data

Tony Song, Dec 2011

Model simulation of the March 11, 2011 tsunami, generated from 1,200 GPS offset data and synchronized with actual

satellite tracks (Jason-1 and Jason-2).

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Matching Models With Satellite Data

Tony Song, Dec 2011

NASA’s Jason-1 satellite was at the right place at the right time and observed the merged waves

Track1 observed tsunami height ~30 cm

Track2 observed tsunami height ~70 cm

Track3 observed tsunami height ~30 cm

Data Model

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Seafloor Topography Is the Cause of the Tsunami Merge

Tony Song, Dec 2011

Tsunami maximum height:

Tsunami maximum height over topography:

Mid-Pacific Mountains

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Summary

Tony Song, Dec 2011

1. For the first time, satellite observations clearly confirm the

existence of merging tsunamis on the open ocean.

2. These merging tsunamis, doubling the tsunami height before reaching shore, are the cause of far-field damages.

3. The potential of merging tsunami jets should be taken into consideration in mapping coastal tsunami hazards and assessing risk levels for coastal facilities.

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Matching Models With DART Buoy Data

Tony Song, Dec 2011

Related Publications Song et al., The 26 December 2004 tsunami source estimated from satellite radar altimetry and seismic waves,

GRL, 32, doi:10.1029/2005GL023683 (2005). Song, Y.T., Detecting tsunami genesis and scales directly from coastal GPS stations, GRL, 34,

doi:10.1029/2007GL031681 (2007). Song et al., The role of the horizontal impulses of the faulting continental slope in generating the 26 December

2004 tsunami, Ocean Modell., doi:10.1016/j.ocemod.2007.10.007 (2008). Song, Y.T. and S.-C. Han, Satellite observations defying the long-held tsunami genesis theory, DOI 10.1007/978-3-

642-16541-2, Springer-Verlag Berlin Heidelberg (2011).